First Drive: BMW i8 Roadster

It can be driven entirely electrically, by a hybrid mix of petrol and electric power, or predominantly by its three-cylinder, turbocharged petrol engine boosted by energetic bursts of electric zest. This highly sophisticated powertrain is enclosed within an immensely strong and dramatically sculpted confection of lightweight carbon fibre and aluminium. It’s the most advanced, ingenious and intriguing production car BMW has ever offered.

There’s now an i8 offering still more transformation options via an electrically opening roof. At its most unexpected, the open-roof i8 amplifies the counter-intuitive experience of a near-silent sportscar. If you’re hard-charging, the 1.0 litre three-cylinder can be more completely heard convincingly masquerading as an engine decidedly more potent, while a more subtle transformation can be provided by dropping the i8 Roadster’s vertical rear window, which provides buffet-free fresh air with the roof up, and an extra swirl of cool on a hot, open-top day.

Designing flaw-free convertibles is never easy. The car’s body mustn’t quiver weakly at the removal of its lid. The roof must remove itself swiftly, silently and with a minimum of operator effort, while stealing a minimum of space, and repel water and wind when it’s sat over your head. These challenges and more are hard enough to meet when a car’s designers engineered its body to accommodate a roofless version in the first place. The task is even harder if that plan was never made. And surprisingly, it wasn’t in the case of the i8 Roadster. Why? Because BMW calculated that the relatively small sales of this car would fail to pay off the massive costs of developing it in the way that a BMW Group model is usually birthed. Which involves a thorough, highly planned, multi-disciplinary approach involving hundreds of people, thousands of hours of computing time and more.

But there was another way. Which was to assemble a small, modestly budgeted project team whose first act was to saw the roof off an i8 Coupe to see what the result would be. Brutal, but a lot cheaper than theorising the effects on computers. The car drove well, its carbonfibre structure evidently able to handle the loss of strength and crash tests that came next. There were many more problems to overcome, not the least the broiling of occupants via the air extractors in the bonnet – now closed off – and a pesky pair of rattling speaker grilles, but the result is thoroughly polished, roofless i8 with a rear-end look all its own. You lose the small rear seats, but little else in the transformation. While they were at it, the team made useful improvements to the i8 itself, not the least being a rough doubling of its electric range to 31miles, the scope to drive it at up to 75mph (briefly) on volts alone, a 12bhp increase in the electric motor’s output to 141bhp for a combined 369bhp and some refinements to the car’s steering and suspension, changes also applied to the Coupe.

They make the i8 more convincing as an electric car and more enjoyable as a convertible, your stealthy progress allowing you to hear the countryside, or a town, as you drive through it. But if you want to feel the full force of this BMW’s 4.6 seconds to 62mph performance, a switch to sport mode and a determined right foot deliver the performance experience you’d expect of a car that looks this speedy. With it, you’ll hear the three-cylinder’s unexpectedly potent bellow besides feeling the rush of wind, though not so much that the sensation is blusteringly unpleasant.

BMW’s minor suspension rethink has certainly improved the i8, reducing much of the understeer uncovered when assaulting tight bends, the steering feeling more precise too, if still short of the tyre-meshing-with-Tarmac sensations that a Lotus can provide. But the Roadster’s chassis balance, responsiveness and reliably sticky grip allow for memorably rapid country road drives. A shame that the fat front pillars invade your vision, though, and reversing soon underlines the need for the parking camera, the view rearwards almost obliterated by the car’s structure. The i8 is wide, too, making this a sometimes cumbersome car in confined spaces. Brakes that are sometimes difficult to apply smoothly at low speeds, too large a gap between second and third gear and the i8’s undersized instruments are further minor gripes.

None of which alters the fact that this is a car whose engineering is as fascinating as its look, nor that it’s beautifully furnished, additively quick, agile, versatile (for two) and makes an environmental impact far more modest than its looks. The open-air conversion sacrifices almost nothing other than the Coupe’s near-pointless rear seats and the addition of a modest 60kg, making a still more appealing machine of the i8. The keenest of keen drivers may still prefer a Porsche 911, but if you want proof that green sportscars can thrill, this is it.

The Numbers

Engines: 1.5 litre three cylinder petrol, electric motor

Transmission: 6-spd automatic 4WD

Bhp/lb ft: 369bhp/236lb ft

0-62mph: 4.6sec

Top speed: 155mph

Price as tested: £124,730